glamor: Handle GL_OUT_OF_MEMORY from glTexImage

[Eric Anholt]

One of the troubles vc4 has with doing X with glamor is that we've
only really got 256MB to play with.  It's pretty easy to run out of
that, particularly with glamor's FBO cache camping on so much
memory. When we do run out, we get a GL_OUT_OF_MEMORY error from
either a TexImage call or a glBufferData call.  This series covers the
TexImage case, avoiding crashes in that path

I've tested it with piglit's xts-render on an i965 driver that throws
GL_OOM on every third glTexImage call.  One new test (rendercheck's
large_blend_src) fails compared to a working i965 on server master,
but the series doesn't make it worse.

The code can be found on the glamor-gloom branch of my tree.